Security Advisory 2020-02-21-1 - ppp buffer overflow vulnerability (CVE-2020-8597)

DESCRIPTION
A remotely exploitable vulnerability was found in Point-to-Point Protocol Daemon (pppd), which has a significant potential impact due to the possibility of remote code execution prior to authentication.

OpenWrt by default enables the _FORTIFY_SOURCE=1 compiler macro which introduces additional checks to detect buffer-overflows in the standard library functions, thus protecting the memcpy() abused in this overflow, preventing the actual buffer overflow and hence possible remote code execution by instead terminating the pppd daemon. Due to those defaults the impact of the issue was changed to a denial of service vulnerability, which is now also addressed by this fix.

CVE-2020-8597 has been assigned to this issue.

REQUIREMENTS
In order to exploit this vulnerability, a malicious attacker would need to provide specially crafted EAP Request packet of type EAPT_MD5CHAP to ppp running in client mode and thus overflowing the rhostname string buffer by providing a very long hostname.

MITIGATIONS
To fix this issue, update the affected ppp package using the command below.

 opkg update; opkg upgrade ppp

The fix is contained in the following and later versions:

• OpenWrt master: 2020-02-20 reboot-12255-g215598fd0389

• OpenWrt 19.07: 2020-02-20 v19.07.1-17-g6b7eeb74dbf8

• OpenWrt 18.06: 2020-02-20 v18.06.7-6-gcc78f934a946

AFFECTED VERSIONS
To our knowledge, OpenWrt versions 18.06.0 to 18.06.7 and versions 19.07.0 to 19.07.1 are affected. The fixed packages will be integrated in the upcoming OpenWrt 18.06.8 and OpenWrt 19.07.2 releases. Older versions of OpenWrt (e.g. OpenWrt 15.05 and LEDE 17.01) are end of life and not supported any more.

CREDITS
This issue was identified by Ilja Van Sprundel and code fix was implemented by Paul Mackerras.